Traumatic brain injury (TBI) is the signature wound of Veterans returning from Operations Iraqi Freedom, Enduring Freedom and Operation New Dawn (OIF/OEF/OND), with up to 20 percent experiencing persistent post-concussive symptoms. Among those with a mild TBI (mTBI) diagnosis, the majority also suffers from stress-based psychopathology, including depression, post-traumatic stress disorder, and other anxiety disorders, as well as chronic pain. Poor management of multiple conditions results in increased morbidity and mortality, increased risk for suicide, and significantly decreased quality of life. Importantly, the association between seeking mental health care and stigma among Veterans is high. Veterans are often unwilling to seek mental health services due to concern that receiving such care would negatively impact their careers and the belief that they should be able to overcome psychological difficulties on their own. Furthermore availability of specialty services is limited for Veterans living in rural settings. Thus the challenge for treatment providers is to provide a unified, efficient, accessible, and acceptable intervention for Veterans with these interdependent systemic comorbid concerns. Acceptance and Commitment Therapy (ACT) is a trans- diagnostic (i.e., applies to more than one diagnosis) behavioral intervention aimed at helping individuals develop the skills needed to pursue valued goals and directions in the face of life's challenges. It provides a unified model of behavior change that has shown promise in treating depression and anxiety, as well as chronic medical conditions. Importantly, ACT has been effectively implemented in various treatment-delivery formats, including 1-day workshops. This flexibility in delivery format allows focus to be placed on how best to package and deliver the intervention to meet the needs of this Veteran patient population, to ensure treatment adherence, and also to increase chances of dissemination into clinical settings. Providing a 1-day ACT ?workshop? for Veterans with mTBI, pain, and mental health problems will allow unitary comprehensive care for the range of emotional, physical, and cognitive symptoms experienced by these Veterans. Presenting the treatment as a ?workshop? rather than ?therapy? will also be better suited for the Veterans who may not be explicitly seeking specialized mental health care. Finally, a 1-day workshop ensures treatment adherence and completion, the lack of which is often the greatest obstacle to effective delivery of mental health services. The aims of this study are to 1) develop a 1-day (5-hour) ?ACT on Life? workshop plus an individual booster session tailored specifically for Veterans with mTBI, stress-based psychopathology, and pain. A multi- disciplinary team of a clinical psychologist, neuropsychiatrist, cognitive psychologist, chaplain, and anthropologist will provide expert input for use in producing the therapist intervention and patient manual; 2) enroll 10 Veterans with mTBI, stress-based psychopathology, and pain in the ?ACT on Life? workshop to obtain qualitative and quantitative feedback from Veterans about the intervention; use Veteran feedback to refine the treatment procedures and manuals; and examine feasibility and acceptability of the intervention; and 3) randomize 30 Veterans with mTBI, pain, and stress-based psychopathology to the refined ?ACT on Life? workshop or to Treatment as usual (TAU) to examine the preliminary efficacy of the intervention on quality of life and functioning, stress-based symptoms of psychopathology, and pain interference.